The present invention relates generally to filter cleaning systems, and more particularly provides a unique automatic cyclic filter backflushing system in which the system lapse time and backflushing pressure may be selectively and independently varied, and the cyclic backflushing valve control portion thereof is automatically reset in a substantially improved manner, after the opening of each of the backflushing valves, using pressurized air cyclically received in and discharged from a reset storage reservoir.
The series of filter elements typically incorporated in a variety of particulate filtration systems, such as dust collection systems and the like, are commonly cleaned utilizing automatic filter backflushing systems which intermittently and quite rapidly discharge essentially the entire volume of pressurized air temporarily held within a main storage tank through one of a series of quick-opening backflushing valves each operatively associated with one of the filter elements or an interior segment thereof.
Opening of a particular backflushing valve creates from tank air discharged therethrough a high pressure, short duration air burst which flows in a reverse direction through the interior of the filter element to dislodge built-up particulate matter adhering to and impeding air flow through its exterior surface. A variety of automatically resettable cyclic control devices are utilized to open the backflushing valves in a predetermined sequence, with the tank being suitably recharged between the successive openings of different ones of the backflushing valves. Particularly effective automatic cyclic filter backflushing systems of this general type are disclosed and described in my U.S. Pat. Nos. 4,465,497 and 4,690,166.
In systems of this general character, there are four operational design criteria which are of particular importance: (1) the source and control of pressurized system-operating air supplied to the main storage tank, (2) control of the system backflushing pressure, (3) control of the system "lapse time" between the sequential openings of the backflushing valves, and (4) the resetting of the cyclic control device after each backflushing valve opening. To essentially maximize the applicational and operational flexibility of an automatic cyclic filter backflushing system it would be desirable to combinatively incorporate therein the ability to utilize as its backflushing and operating pressure source either an available, in-place pressurized air source (such as the typical, approximately 90 psig air commonly used to power pneumatic hand tools) or a dedicated system air compressor, the ability to selectively and independently vary both the system backflushing pressure and its lapse time to thereby accommodate the sometimes widely divergent flushing pressure and frequency requirements of different particulate filtration systems, and the ability to reliably reset the cyclic control device of the system without resort to often failure-prone electrical or mechanical devices, or pneumatic methods vulnerable to disturbances in the main pressurized supply air flow to the storage tank.
Conventional automatic cyclic filter backflushing systems have proven to be deficient as to at least one of the aforementioned design criteria. For example, the system disclosed in my U.S. Pat. No. 4,465,497 provides for selective variation of its backflushing pressure, but is specifically designed and operative to maintain an essentially constant lapse time which is unchanged by adjustments to the system's backflushing pressure. Further, the sequential resetting of the system's cyclic control device is pneumatically achieved utilizing, in opposition to each other, portions of the incoming tank supply air. In addition to being a somewhat inefficient method of resetting the cyclic control device, this technique also creates the possibility of disrupting the important reset process in the event that the main air supply to the system is disturbed in some fashion. The system set forth in my U.S. Pat. No. 4,690,166 is dependent upon a separate air compressor for its main air supply, and utilizes an internal spring element in its cyclic control device for reset purposes. Failure of this single spring element can render the entire system inoperative.
It is accordingly an object of the present invention to provide an improved automatic cyclic filter backflushing system which combines all of the aforementioned desirable system capabilities to thereby eliminate or at least substantially minimize the applicational and operational limitations commonly associated with conventional systems of this type.